1. Field of the Invention
The present invention relates to drilling fluid telemetry systems, and, more particularly, to a system and method for reducing pump noise in a received telemetry signal.
2. Description of the Related Art
Drilling fluid telemetry systems, generally referred to as mud pulse systems, are particularly adapted for telemetry of information from the bottom of a borehole to the surface of the earth during oil well drilling operations. The information telemetered often includes, but is not limited to, operational parameters, such as, pressure, temperature, direction and deviation of the wellbore. Other parameter include logging data such as resistivity of the various layers, sonic density, porosity, induction, self potential and pressure gradients related to the reservoirs surrounding the wellbore. This information is critical to efficiency in the drilling operation and economic production of the reservoirs.
A number of different pulser types are known to those skilled in the art. These include, but are not limited to, poppet pursers for generating positive or negative pressure pulses; siren pursers for generating continuous wave pulse signals; and rotationally oscillating shear-valve pursers that may generate discrete pulses and/or continuous wave signals. Various encoding techniques are known in the art for transmitting data utilizing the described pulse signals. In general, all of these systems generate a pressure pulse by blocking or venting a portion of the drilling fluid flowing in the drill string to the bit. The generated pulse propagates to the surface where it is detected and decoded for further use. A major source of noise in the detected signal is a result of the large pressure pulses associated with the use of positive displacement, plunger type pumps utilized for pumping the drilling fluid through the system. Such pumps commonly generate pressure pulses 1-2 orders of magnitude greater than the detected pressure signals at the point of signal detection. In addition, the pump frequency is commonly within the range of the pulsed signal frequency.
The system and method of the present invention operate to reduce the pump noise in the received signal and provide enhanced signal detection and reliability.